1. Field of the Invention
The present invention relates to a hard film which covers the surface of a tool and a hard film-coated tool having said hard film.
2. Description of the Related Art
Coating with a hard film of TiN, TiC, TiCN, TiAlN, or the like has been a common practice of improving the wear resistance of cutting tools, such as chips, drills, and end mills, and jigs, such as presses, forging dies, and punches, which are made of cemented carbide, cermet, high-speed cutting steel, or the like. Typical of such hard film is composite nitride film (TiAlN) composed of Ti and Al. Because of its excellent wear resistance, it is superseding conventional hard films of titanium carbide, nitride, or carbonitride mentioned above, and it is finding application to high-speed cutting tools and cutting tools for hard materials such as quenched steel.
Notable among the above-mentioned TiAlN coating films characterized by high hardness and excellent wear resistance is the one which has the crystalline structure of NaCl type and hence excels in oxidation resistance at high temperatures. (See Patent Document 1 below.)
There has also been proposed a new coating film with improved wear resistance which is composed of TiAlN and additional Cr, the latter contributing to the increased Al content and the increased hardness and oxidation resistance while retaining the rock salt crystalline structure (cubic crystal) for high hardness. (See Patent Document 2 below.) Other coating films proposed so far include the one composed of TiCrAlN and additional Si and B for improved oxidation resistance (see Patent Document 3 below) and the one composed of CrAlN and additional Nb, Si, and B for improved oxidation resistance (See Patent Document 4 below).
Patent Document 1:
                Japanese Patent No. 2644710 (Paragraphs 0011-0018)Patent Document 2:        Japanese Unexamined Patent Application Publication No. 2003-71610 (Paragraphs 0018-0023)Patent Document 3:        Japanese Unexamined Patent Application Publication No. 2003-71611 (Paragraphs 0023-0029)Patent Document 4:        International Publication No. 06/005217 (page 3, line 30, to page 9, line 31).        